Critical role of bicarbonate and bicarbonate transporters in cardiac function

Figure 2 Isolated myocytes exhibit greater contractility in CO₂/HCO₃^- buffer than in HEPES buffer. Ventricular myocytes from rat hearts were enzymatically dissociated using Langendorff perfusion[104] and myocyte mechanics were analyzed at room temperature (24 °C), with stimulation at 0.5 Hz as described previously[107]. Myocytes were switched between HEPES-buffered Tyrode’s solution (in mmol/L: NaCl 140, KCl 5.4, MgCl₂ 1, CaCl₂ 1.8, glucose 10, and Na-HEPES 5; pH = 7.4; bubbled with 100% O₂) and HCO₃^--buffered Krebs solution (in mmol/L: NaCl 120, NaHCO₃^- 25, KCl 4.2, KH₂PO₄ 1.2, MgCl₂ 1, CaCl₂ 1.8, and glucose 10; pH = 7.4 when bubbled with 95% O₂ and 5% CO₂). A: Representative contraction tracing of a myocyte bathed in HEPES buffer, then switched to HCO₃^- buffer, and then returned to HEPES buffer; the lower tracings show an expanded scale for the indicated (a-d) time points. The lower panels show the time course of fractional shortening (B) and average fractional shortening (C) of myocytes (n = 19) in HEPES buffer and then switched to HCO₃^--containing buffer. Experiments were performed using myocytes from 3 hearts and statistical analysis was conducted using a paired t-test. Values are means ± SE.